1. Field of the Invention
The present invention relates generally to an electrostatic opposing field spectrometer and, more specifically, to an electrode arrangement for such spectrometer.
2. Description of the Prior Art
The functioning of integrated circuits is usually automatically checked with computer controlled test installations. In most instances, however, such tests are incomplete since perceived faults in the integrated circuits are difficult to localize. Additional measurements must therefore be performed inside of the integrated circuits, particularly during the development phase. Electron beam test instruments which test non-destructively and without contact are particularly well suited for such tests and are being increasingly used in all areas for the development and manufacture of micro-electronic components.
Particularly good information for localizing faults in large scale integrated (LSI) circuits are obtainable from quantitative waveform measurements at selected nodes of the components during testing. For example, a primary electron beam generated in an electron optical column of a modified scanning electron microscope is positioned at a measuring point and the shift of the energy distribution of the secondary electrons triggered at the measuring point is identified in a spectrometer. The energy shift is dependent upon the voltage, or potential, of the component measuring point.
The publication of H.P. Feuerbaum in "SEM/1979/I, SEM Inc., ANF O'Hare, Illinois, 60666", pages 285-296 discloses an electrostatic opposing field spectrometer. The spectrometer includes a deflection element disposed above an extraction and retarding field electrode. Any secondary electrons which are on axially remote paths in the proximity of the housing parts are only weakly deflected by the deflection element due to its asymmetrical structure and do not contribute to the measured signal of the secondary electron detector. Low secondary electron currents lead to poor signal-to-noise ratios and limit the resolution with which voltages, or potentials, can be measured.
U.S. Pat. No. 4,464,571 discloses an electrode arrangement for an opposing field spectrometer which generates a spherically symmetrical opposing field.